Superplasticizers acrylate based

An optimization of mortar mixture proportions was carried out on mortars prepared with 10% waste particles, by adding a limestone powder as filler, at a dosage of 20% by weight of cement, replacing quartz sand, in order to improve the mortar mechanical performance. Limestone powder was added with and without an acrylic-based superplasticizing admixture, at a dosage of 1.0% by weight of cement. 

The poly-aryl sulphonate type superplasticizers have been widely used. However, for the last 20 years many new types of superplasticizers have been put into use. They are the derivatives of acrylic, methacrylic and maleic acids. Acrylate-based... 

Higher than normal workability of concrete containing a superplasticizer is maintained for about 30-60 minutes, and then there is a rapid decrease in slump, termed slump loss. To control or extend the workability, the superplasticizer should be added at the point of discharge of concrete. Some admixtures are added to superplasticizers to control slump loss. The acrylate-based superplasticizers are claimed to possess good slump retention qualities. 

With the advent of high-performance concrete and the development of third-generation (mostly acrylic polymer-based) superplasticizers which provide significantly higher water reduction at flowable consistencies, this demarcation has blurred. Through the use of a mixture of admixtures it is now possible to obtain highly durable low water-cement ratio concretes that are nearly self-leveling and yet quite cohesive. 

One of the significant limitations of the use of first- and second-generation superplasticizers in ready-mixed flowing concrete is the rapid decrease in the initially achieved high workability and this constitutes one of the chief constraints to their wider acceptance. Therefore, a number of major producers of admixtures have sponsored active research to improve the workability retention characteristics of their superplasticizers. Some recent developments [48] have shown promise, among these are materials based on acrylate polymers (AP). The AP-based materials are reported to be more effective than SNF- or SMF-based surplasticizers in terms of water reduction, slump increase and slump retention. Figure 7.19 shows the remarkable improvement in the retention of workability produced by the AP type superplasticizer compared to an SNF type. 

Cabrera and Lynsdale investigated the effect of superplasticizers based on modified lignosulfonate, SNF, SMF, and acrylic acid-hydroxypropyl methacrylate on the hydration of cement. The DTG/TG techniques were adopted. There was a slight acceleration of hydration in the presence of admixtures at 1 day, but the long-term hydration was not affected. 

An extensive work was carried out by Uchikawa l on the conduction calorimetry of superplasticizers, such as SNF (NS in the figure), lignosulfonate (LS), a co-polymer of acrylic acid with acrylic ester (PC), and a three dimensional polycondensate product of aromatic aminosulfonic acid with trimethyl phenol (AS) (Fig. 11). The first peak in the calorimetry corresponds to the heat of dissolution of alite, the heat of formation of the AFt phase, and the calcium hydroxide formation from free lime. The second peak corresponds to the heat of hydration of alite. The admixtures were found to accelerate the formation ofthe ettringite phase. At w/cratios ofO.3 and 0.5 and a later addition of the admixture, the appearance of the second peak was significantly delayed and the peaks were of lower intensity. Most retardation occurred with polycarboxylic acid and amninosulfonic acid-based admixtures (Fig. 11). DSC was used to determine the amount of lime formed at different times. The DSC results show that the addition of admixtures at different w/c ratios generally decreases the amounts of lime in the presence of superplasticizers (Fig. 12). 

---